Head teachers should carefully audit behaviour policies to ensure they do not clash with equalities legislation and lead to certain groups being unfairly targeted, it is claimed.

In a report, Dr Maggie Atkinson warned that a minority of schools were still “directly or indirectly” discriminating against pupils by race, religion or gender.

The study said that harsh rules on hairstyles unfairly affected black boys who are more likely to wear corn rows.

It also suggested that schools should be weary of excluding children from certain backgrounds for failing to show “intergenerational respect” to adults because this can be shown in ways “that are not always the same as they are in white English society”.

It came as figures showed that children – particularly boys – from some ethnic backgrounds were more likely to be excluded than others.

Gypsy, Roma and Irish Traveller children were four times more likely to be expelled, and Black Caribbean pupils were three times more likely, the report found.

It also emerged that pupils with special needs are for more likely to be targeted than other children. In all, children with behavioural or learning problems are nine times more likely to be excluded than their classmates, it emerged.

The report – published following a lengthy investigation into exclusion practices by English schools – recommended that Ofsted should assess head teachers’ attitudes to “inclusion and meeting the needs of a diverse pupil population”.

It said it would also shop schools operating discriminatory exclusion policies to Ofsted and local councils to prevent “grave inequality in the treatment of children and a denial of their rights to education”.

“We expect the authorities to take immediate and appropriately robust steps to ensure that such activity no longer takes place,” said the report said.

But the conclusions were criticised by the Association of School and College Leaders amid claims schools alone could not address the issue.

Brian Lightman, general secretary, said: "Exclusion is a last resort when all other sanctions have failed. It is a sad fact that in some cases, exclusion is in the best interest of the child as the specialist support they so badly need is only made available when they are no longer in school.

"It is not a failure of schools to understand pupils' cultural needs that leads to exclusion.

“Of course it is concerning that some groups of pupils are excluded more than others but this reflects deep seated issues in our society which schools alone cannot solve alone.”

The report said that the “vast majority” of schools had “inclusive, non-discriminatory” exclusion policies.

But it warned that this was “not the case” in a small minority of schools investigated by officials. Examples of “discriminatory and therefore illegal” practice included:

•The exclusion of children for hairstyles that are overwhelmingly worn by black boys, for example corn rows;

• Rules of dress, appearance and conduct that apply differently to boys than they do to girls;

• Rules that take little or no account of differences in “intergenerational respect and how it is to be shown by children in ways that are not always the same as they are in white English society”.

It also said that schools were disproportionately excluding children from school – or forcing them to be taught separately from peers – when they have special needs.

Dr Atkinson said: "We have found that the most important single thing a school can do is to realise that some children need more support than others in school, and to meet this need.

"The best schools do this instinctively because they realise that this is core to their job, rather than an 'optional extra'.”